In case you’re one of the few who missed it, Wizards of the Coast has finally joined the Information Age and decided to make all old D&D editions available for sale electronically at D&D Classics. (It’s a white label DriveThruRPG/RPGNow site.) B1: In Search Of The Unknown is free for their launch week!
They have loads of the classic modules up already and they say they plan to get everything up there eventually. Good on them!